ICs comprise a complex assortment of microminiature electronic components on a silicon chip. To protect them from damage due to handling and moisture, ICs are typically housed in a ceramic or plastic package that is either soldered to a PCB or inserted into a matching socket which has been soldered into a printed circuit board. For IC housing, ceramic is the material favored in high reliability industrial and military applications; plastic, being less costly, is favored in commercial and consumer products. Many millions of these types of structures are manufactured every year, worldwide. For the PCB substrate, FR4 resin laminate is becoming an industry norm because of its electrical, chemical and physical properties and its low cost.
Means by which the IC package has been attached electronically to a PCB or another IC include metal pins in plastic pin grid array (PPGA), silk screened solder paste, solder preforms and solder balls. Injection molded techniques have been used in some cases to apply solder. In PBGA, solder balls are heated to a temperature at which it will reflow, and the solder is applied to contact pads on the PCB, also referred to herein as lands, electrically connecting the IC to the PCB. Some of the plastic packages have material sculpted out from the middle to form a recess in which the IC die will be placed when the plastic parts are laminated together. After the IC die is installed in the package, electrical connections are made to the die contact pads and to solder through the conductive metal patterns within the package. These soldering processes may involve two reflow heating steps, the first reflow to attach solder at selected peripheral points on the surface of the laminate, and the second reflow to reshape the solder to a sphere.
U.S. Pat. No. 4,585,157 to Stephen R. Belcher describes a method of bonding two IC chips face-to-face in a type of lead frame wire bonding called tape automated bonding (TAB). Rather than testing a chip at a site on the lead frame, the patented method uses a tape bonding approach wherein the finger leads at a single site in a lead frame are divided into two groups and are bonded in two separate compression bonding processes. In the second bonding process, the first chip is flipped upside down and fit into a recess in a second thermode. The present invention is not directed to TAB, but rather is directed to a means and process of delivering discrete amounts of solder in PBGA to connection lands on a PCB having an IC mounted thereon.
U.S. Pat. No. 5,979,664 to Alan M. Lyons et al describes a method of treating solder used in mounting an IC to a PC board in order to eliminate oxide at the solder surface without flux. To remove the oxide without flux, nitrogen or argon gas is flowed over the heated areas being joined. Unlike the present invention, the patent is not directed to the solder delivery itself, and in particular not directed to a solder injection mold delivery system and process.
U.S. Pat. No. 5,244,143 to Ference et al, assigned to the same assignee as the present invention, describes various embodiments of injection mold apparatus for solder. In the present invention, an injection mold apparatus for use with PBGA is described and a process set forth which is particularly adapted to PBGA. The patent is useful for its description of the solder reservoir.
U.S. Pat. No. 5,551,148 to Kazui et al describes a flexible film having tapered through-holes filled with solder, which is heated and transferred under pressure from the larger diameter end of the through holes to a circuit board as bumps on pads. The transfer of solder is no good if the pressure is too low. At that point the flexible film is removed either by dissolving in hydrazine or ethylene diamine, sublimated by the heat of the soldering process, or peeled away. The solder injection mold of the present invention is not a flexible film, but a sturdy, reusable transfer device. Since it does not have to be dissolved, sublimated or peeled away, there is no handling of harsh chemicals or destruction or distortion of the injection mold used in the present invention.
None of the above references addresses the problems, achieves the results or discloses the process and apparatus of the present invention.